fix: preserve quote formatting for image tags also

[consideRatio]

This PR in practice reverts #16 which was introduced due to a bug fixed in ruamel.yaml 0.15.44. For more details see #113, but the gist of it is that there is a difference between ruamel.yaml version 0.15.43 and 0.15.44 that makes us no longer need a previously added workaround to manage the 0.15.43 behavior.

pip install "ruamel.yaml==0.15.43" && \
python -c "import sys; import ruamel.yaml; ruamel.yaml.YAML(typ='rt').dump({'x': '008'}, sys.stdout)"
        
pip install "ruamel.yaml==0.15.44" && \
python -c "import sys; import ruamel.yaml; ruamel.yaml.YAML(typ='rt').dump({'x': '008'}, sys.stdout)"

Closes #113

Motivation

@manics and I are working to setup pre-commit to autoformat yaml files, and chartpress coercing the image tags to single quotes for no good reason is disruptive for us. See jupyterhub/zero-to-jupyterhub-k8s#1996 (comment).